USB: adutux: fix NULL-derefs on disconnect

The driver was using its struct usb_device pointer as an inverted
disconnected flag, but was setting it to NULL before making sure all
completion handlers had run. This could lead to a NULL-pointer
dereference in a number of dev_dbg statements in the completion handlers
which relies on said pointer.

The pointer was also dereferenced unconditionally in a dev_dbg statement
release() something which would lead to a NULL-deref whenever a device
was disconnected before the final character-device close if debugging
was enabled.

Fix this by unconditionally stopping all I/O and preventing
resubmissions by poisoning the interrupt URBs at disconnect and using a
dedicated disconnected flag.

This also makes sure that all I/O has completed by the time the
disconnect callback returns.

Fixes: 1ef37c60 ("USB: adutux: remove custom debug macro and module parameter")
Fixes: 66d4bc30 ("USB: adutux: remove custom debug macro")
Cc: stable <stable@vger.kernel.org>     # 3.12
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190925092913.8608-2-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/adutux.c

@@ -75,6 +75,7 @@ struct adu_device {
 	char			serial_number[8];
 
 	int			open_count; /* number of times this port has been opened */
+	unsigned long		disconnected:1;
 
 	char		*read_buffer_primary;
 	int			read_buffer_length;
@@ -116,7 +117,7 @@ static void adu_abort_transfers(struct adu_device *dev)
 {
 	unsigned long flags;
 
-	if (dev->udev == NULL)
+	if (dev->disconnected)
 		return;
 
 	/* shutdown transfer */
@@ -243,7 +244,7 @@ static int adu_open(struct inode *inode, struct file *file)
 	}
 
 	dev = usb_get_intfdata(interface);
-	if (!dev || !dev->udev) {
+	if (!dev) {
 		retval = -ENODEV;
 		goto exit_no_device;
 	}
@@ -326,7 +327,7 @@ static int adu_release(struct inode *inode, struct file *file)
 	}
 
 	adu_release_internal(dev);
-	if (dev->udev == NULL) {
+	if (dev->disconnected) {
 		/* the device was unplugged before the file was released */
 		if (!dev->open_count)	/* ... and we're the last user */
 			adu_delete(dev);
@@ -354,7 +355,7 @@ static ssize_t adu_read(struct file *file, __user char *buffer, size_t count,
 		return -ERESTARTSYS;
 
 	/* verify that the device wasn't unplugged */
-	if (dev->udev == NULL) {
+	if (dev->disconnected) {
 		retval = -ENODEV;
 		pr_err("No device or device unplugged %d\n", retval);
 		goto exit;
@@ -518,7 +519,7 @@ static ssize_t adu_write(struct file *file, const __user char *buffer,
 		goto exit_nolock;
 
 	/* verify that the device wasn't unplugged */
-	if (dev->udev == NULL) {
+	if (dev->disconnected) {
 		retval = -ENODEV;
 		pr_err("No device or device unplugged %d\n", retval);
 		goto exit;
@@ -764,11 +765,14 @@ static void adu_disconnect(struct usb_interface *interface)
 
 	usb_deregister_dev(interface, &adu_class);
 
+	usb_poison_urb(dev->interrupt_in_urb);
+	usb_poison_urb(dev->interrupt_out_urb);
+
 	mutex_lock(&adutux_mutex);
 	usb_set_intfdata(interface, NULL);
 
 	mutex_lock(&dev->mtx);	/* not interruptible */
-	dev->udev = NULL;	/* poison */
+	dev->disconnected = 1;
 	mutex_unlock(&dev->mtx);
 
 	/* if the device is not opened, then we clean up right now */